This invention deals in the art of beverage dispensers and is most particularly applicable to automatic mixed drink dispensers wherein central reservoirs supply beverages to one or more remote vending stations. One such system is shown in the prior art in applicant's U.S. Pat. No. 3,991,911, for "AUTOMATIC DRINK DISPENSING APPARATUS HAVING PROGRAMMING MEANS." In this prior art teaching, a plurality of reservoirs are provided to maintain the various components capable of being dispensed, such components being dispensed either singularly or in combination. Each of these reservoirs is provided with a pressure sensor 34, shown in phantom in FIG. 2, which fundamentally comprises a pressure switch. In the prior art, this pressure sensor is mounted within the reservoir itself, or along a conduit leading therefrom, in such a manner that when the liquid is at least at a minimum level within the reservoir there is sufficient pressure against the switch to produce an output indicative of that fact. Similarly, when the liquid falls below a minimum level, insufficient pressure bears against the switch 34 such that an output is produced indicating that the reservoir is "empty." In the aforementioned prior art patent, lamps are associated with each of the various reservoirs, the lamps being illuminated by their associated sensor switch when their respective reservoirs are "empty."
While applicant has found the sensor switch 34 to be adequate for purposes of advising a bartender or other user as to the presence of an "empty" reservoir, it has also been found that such sensors are susceptible to false readings. Since the reservoirs of the drink dispensers are generally of a small volume, the variation of pressure between a reservoir maintaining sufficient beverage and one which is "empty" is small. With the sensor switches 34 being mechanical in nature and pressure-actuated, it has been found that the sensitivity thereof is often not sufficient to guard against false readings. On occasion, it has been found that reservoirs maintaining sufficient beverage have resulted in "empty" signals while, on the contrary, reservoirs having an insufficient amount of beverage have failed to render an "empty" signal. The problems are inherently due to the restricted sensitivity achievable with a pressure-actuated electromechanical switch.